<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        div{
            display: inline;
            background-color: red;
            width: 100px;
            height: 100px;
            border: 1px solid black;
        }
        span{
            display: block;
            background-color: red;
            width: 100px;
            height: 100px;
            border: 1px solid black;
        }
    </style>
</head>
<body>
<!--
行内元素  和块级 元素 没有太明显的界限 可以通过displa有属性将二者进行转换-->
<div>
    AAAA
</div>
<div>
   BBBB
</div>
<hr>

<span>ccc</span><span>ddd</span>
</body>
</html>